Television receiver



Nav. 17, 1942. A v, LQUGHREN TELEvIsoN RECEIVER Filed Feb. 7.. 1940 2 Sheets-Sheet 1 Illa..

INVENTOR fTHUR V. LOUGHREN ATTORNEY N0 17 1942 A. v. LouGl-IREN l TELEVISOR RECEIVER Filed Feb. 7, 1940 2 SheetsqSheet 2 INVENTOR UR V. LOUGREN ATTORNEY Patented Nov. 17, 1942 TELEVISION RECEIVER ArthurV. Loughren, Great Neck, N. Y., assignor to Hazeltine Corporation, a corporation of Delaware Application February 7, 1940, Serial No. 317,622

9 Claims. (Cl. 178-7.5)

This invention relates to television receivers and is particularly concerned with such receivers adapted to receive a carrier wave which is amplitude-modulated with video signals and -frequency-modulated with synchronizing signals. This application is a continuation-in-part of applicants copending application Serial No. 212,691, led June 9, 1938, -now Patent No. 2,254,435, granted Sept. 2, 1941.

In accordance with present television practice, there is developed and transmitted a signal ,which comprises a carrier Wave modulated during successive intervals or trace periods by video-frequency signal components representative of light and shade values of an image being transmitted. During retrace intervals between the trace periods, the carrier wave is modulated by synchronizing impulses or components which correspond to initiations of successive lines and fields in the scanning of the image. At rthe receiver, a beam is so deiiected as to scan and illuminate a target in a series of fields of parallel lines, the videosignal components being utilized to control the intensity of the beam. The line-scanning and field-scanning synchronizing components are separated from the video-signal components and from each other and are utilized to synchronize the operation of the receiver line-scanningsand eld-scanning apparatus Wlthsimilar apparatus utilized at the transmitter'indeveloping the signal. The transmitted program pr image is thereby reconstructed on the target of the receiver.

Various types of television signals as well as various types of scanning and synchronizing methods and apparatus have been proposed. For example, in certain systems, negativemodulation is employed, that is, a decrease in carrier amplitude during the trace periods when the carrier is amplitude-modulated by; the video-signal components corresponds to an increase in illumination. In other systems, positive modulation is utilized in which an increase in carrier amplitude corresponds to an increase in illumination. TheA synchronizing-modulation components of the signals used in these systems ordinarily have amplitude values outside the range of the video-moducarrier amplitude While, where positive -modulacreased power, but also due to the fact that interference presented by the signal of one program with another is a function -of the peak value of the power radiation of the signal of the interfering program. y

In television receiving systems noise components disturb b oth the' video-signal and the synchronizing-signal components. noise impulses are represented by increases in carrier amplitude so that in positive modulation systems, the noise components appear in the image as white vspots while in negative modula 'tionl systems they appear as black spots. The White spots are usuallythe more annoying to an observer so that, as far as the video signal is concerned, a negative modulation signal is less affected by noise. On the other hand, with negative modulation, synchronizing components are represented by increases in carrier amplitude and are thus most subject to noise eiects, While with positive modulation, synchronizing components are represented by a reduction of .carrier amplitude, usually to zero, so that they are substantially less aiected by noise. Therefore, as far as the synchronizing' components are concerned, a positive modulation .signal is less affected by no1se.

In applicants above-mentioned copending application, an improved television system is described utilizing a carrier Wave having the desirable characteristics incident to negative modulation with respect to the video-signal components and including synchronizing components which are not appreciably affected by noise disturbances. In accordance with the system of the copending application, there is provided a television broadcasting system which comprises a station for developing and transmitting a modulated-carrier Wave and which includes means for developing suitable video-signal components and synchronizing-signal. components. The carrier Wave is amplitude-modulated in accordance with videosignal components during the trace intervals and is frequency-modulated in accordance with synchronizing-signal components during the retrace intervals. The carrier Wave, for example, normally has a predetermined frequency and is shifted with respect to this frequency during the retrace intervals. A receiver for receiving and reproducing the transmitted wave includes means for amplitude-detecting the carrier wave to derive the video-signal components and means for frequency-detecting the carrier wave to derive the synchronizing-signal components.v

The system specifically disclosed in such copending application is a single-sideband system In generaL,

, ceived carrier-wave amplitude variations.

the receiver that the carrier is transmitted with one-half the over-all gain of the fully-transmitted sideband, in accordance with the general practice in single-sideband systems. If such equalization is not provided, the low-frequency video-signal components adjacent the carrier wave and subject to double-sideband reception are reproduced with a relatively greater amplitude with respect to corresponding components of the televised picture than those subject to pure single-sideband reception. resulting in a distortion in the reproduced picture. However, in such a system, when the frequency of the carrier wave is shifted during the retrace interval to transmit synchronizing-signal information, there is an enective shift of the carrier wave on the sloping portion of the band-pass selector characteristics of the receiver, resulting in amplitude pulses which appear in the video-signal channel of the receiver during retrace intervals, thus rendering it difficult to stabilize the video-frequency signal of the receiver at a signal amplitude corresponding to a given actual shade value of th'ehtransmitted picture, preferably black.

It is an object of the present invention, therefore, to provide an improved television receiver adapted to receive a modulated-carrier wave including video-signal components amplitudemodulated on the carrier wave and synchronizing-signal components frequency-modulated on the carrier wave.

It is another object of the invention to provide a television signal receiver adapted to receive a modulated-carrier wave including video-signal components amplitude-modulated on the carrier wave and synchronizing-signal components frequency-modulated on the carrier wave in which the signal applied to the reproducing device of the receiver is stabilized at a predetermined amplitude level corresponding to a predetermined actual shade value of the transmitted picture, preferably black.

In accordance with the present invention, there is provided a television receiver adapted to receive a modulated-carrier 'wave including video-signal components amplitude-modulated on the carrier wave only during trace intervals and synchronizing components frequency-modulated on the carrier wave only during retrace intervals. The receiver comprises means for detecting and utilizing the frequency-modulated components of the received signal to synchronize the scanning operation of the receiver, means for deriving from the received carrier signal a carrier signal having a peak-amplitude level during the retrace intervals representative of a limiting shade' value of the V`transmitted picture and amplitude-mdulated by the video-signal components during trace intervals, and -means including a reproducing device for detecting and utilizing the amplitude-modulation components of the derived carrier signal,`V the detected amplitudemodulation components being subject to variation in amplitude, in accordance with the re- Also, the means for detecting and utilizing the amplitude-modulated components of the received signal includes means for stabilizing the signal input to the reproducing device at an amplitude level corresponding to the above-mentioned limiting shade value of the transmitted picture.

' In accordance with one preferred embodiment of the invention, the video signal is negatively level corresponding to the actual black shade value of the transmitted picture.

In accordance with another preferred embodiment of the invention, the received video-signal components are positively amplitude-modulated on the signal-carrier wave and stabilization is effected at an amplitude level corresponding to the amplitude-modulated on the carrier wave and stabilization is effected at the signal-amplitude actual white shade value of the transmitted picture. Also, in accordance with a modification of the invention, means are provided in the receiver for relatively equalizing reproduced video-frequency components of the transmitted picture.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the accompanying drawings, Figs. 1 and 2 are circuit diagrams, partly schematic, of complete television transmitting and receiving systems, respectively; while Figs. 3, 4, 5, and 6 are graphs illustrating certain operating characteristics of the systems shown in Figs. 1 vand 2 to aid in the understanding of the invention.

Referring now more particularly to Fig. 1 of the drawings, the television transmitter there represented is generally similar to that of applicants aforesaid copending application and circuit elements which are similar have identical reference numerals. Such television transmitting system comprises a signal-generating device I0 of any conventional design which may include a cathode-ray signal-generating tube having the usual electron gun, photosensitive target and line-scanning and field-scanning elements. There are also provided a line-scanning generator I2 and a field-scanning generator I3 with their output circuits connected directly to the line-scanning and field-scanning elements, respectively, of signal-generating device I0. In order to provide pedestal impulses for blocking out or for suppressing undesired impulses in, and ensuring the proper wave form of, the modulation signal developed by the generator III, there is provided a pedestal-impulse generator I4 having its output circuit coupled to a control electrode of signal-generating device I0. synchronizing-signal generating apparatus is provided for the transmitter of Fig. 1 in accordance with an arrangement to be hereinafter described in detail.

In order to synchronize the operations of the generators I2, I3, and I l and the synchronizingvfilter 2|, a power amplifier 22, and an antenna system 23, 24.

Neglecting for the moment the details of the stages I9, 20, and 2| and the synchronizing-signal generating apparatus presently to be described, the system just described includes the apparatus of a television transmitting system of conventional design, those parts of the system illustrated schematically being of any well-known suitable construction so that a detailed descripvtion of thesystem and its operation is unnecessary herein. Briefly, however, the image of the scene to be transmitted is focused on the target of the cathode-ray tube of signal-generating device I in which a cathode ray is developed, accelerated, and also focused on the target. Scanning or deflection waves developed by the generators I2 and I3 are applied to the scanning elements of the signal-generating device I0 and serve to deflect the ray to scan successive series of fields of parallel lines on the target. Pedestal signal-generating device I0 being electrically affected to an extent depending upon the varying values of light and shade at corresponding incremental areas of the image focused thereon as the cathode rayscans the target, a voltage of correspondingly varying amplitude is developed in the output circuit of the signal-generating tube and applied to ampliler I6. Suitable timing or synchronizing impulses are applied from generator I5 to the generators I2, I3, vand I4 to maintain these generators in synchronism with either the master frequency, in case of direct camera shots, or'the motion picture camera, in the case where such pictures are being transmitted. The video-signal components applied to the amplifier i6 are amplified therein and thereupon supplied to the modulator II wherein they are impressed on the carrier wave generated by the oscillator I8. The signal is translated from the modulator i1 to the power amplifier 22 by way of stages I9-2l, inclusive, to be described hereinafter, wherein the synchronizing-signal components are added to the carrier wave. The heterodyne-frequency lter 2l is of any suitable conventional type designed to pass either the differ- 3|. Preferably, the oscillator is of the push-pull type comprising vacuum tubes 32 and 33 having their input circuits connected in push-pull relation by way of an inductance 34, a leak resistor 35, and a grid condenser 35a being connected in parallel between the mid-tap on the inductance 34 and the cathodes of the tubes. Theanode circuits of tubes 32 and 33 are also connected in push-pull relation by way of an inductance 36 coupled to the inductance 34 as indicated by bracket M, a mid-tap on the inductance 36-being connected to the cathodes of the tubes by way of a suitable'anode-voltage supply, such as a battery 31. The inductance 36 is normally sharply tuned to a fixed frequency by means of a condenser 33 or other suitable circuit arrangement such that theoscillations developed by the oscillator 30, when combined with the carrier wave developed by oscillator I8, produce a heterodyne component of the desired carrier frequency for transmission. An inductance 39 is coupled to inductance 36 and connected to the frequency changer 20 for the purpose of shifting the carrier frequency of the signal derived from the filter I9 in accordance with the frequency of the oscillations developed by the oscillator 30.

The frequency-adjusting network 3| preferably comprises a pair of vacuum tubes 40 and 4I having their control grids connected by way of resistors 42 and 43 to the output circuits of the linescanning generator I2 and field-scanning generator I3 in parallel by wayv of condenser 44, which is effective to by-pass oscillation-frequency currents to ground. The control grids of tubes 40 and 4I are also connected by way of coupling condensers 45, 46 to their respective anodes.

which, in tum, are connected to the terminals tri an inductance 41. The inductance 41 is connected in push-pull relation in the anode circuits of the tubes, a mid-tap thereof being connected to the tube cathodes by way of a suitable anodevoltage supply source indicated by battery 43. The inductance 41 is inductively coupled to the inductance 36 of the oscillator frequency-determining circuit.

In considering the operation of the transmitter just described and referring first to frequencyence or sum frequencies developed in frequency of these generators and of the same frequencies.

These impulses are timed to fall within and have durations somewhat less than the line-retrace and field-retrace periods, respectively, the generated line-frequency pulses being of substantially greater amplitude than the generated fieldfrequency pulses, as illustrated. Generators I? and i3 are provided vwith output circuits which are coupled to a control apparatus 29 for the purpose of shifting the frequency of the carrier wave impressed upon the frequency changer ifi from the lter i9. Control apparatus 29 includes an oscillator indicated generally at 3@ and a frefluency-adjusting network indicated generally at adjusting network 3l which, itv will be assumed, is excited from oscillator 3U, it will seen that, since the impedances of condensers '55 and 46 are high compared with those of resistors 42 and 53, the voltages' across the resistors lead the voltage across the inductance ll by a large angle and that the space currents of the tubes, being in phase with the tube input voltages, also lead the voltage across inductance il in corresponding degree. Hence, the system simulates an impedance having primarily capacitive reactance, the value of which varies in accordance with the grid-bias voltage applied to the tubes. Adjustment of the grid-bias voltage on the tubes ll@ and dll, therefore, varies `the effective reactance of the circuit 3i and, hence, the natural frequency of the oscillation circuit 36, 39 to which it is coupled.

Normally, the tubes 6l@ and il are biased beyond cutoff and remain'so biased during the video-signal or trace periods, being rendered operative only during synchronizing or retrace periods when impulses from one or both of the generators i2 and i3 are applied thereto. Since the tubes lil and ii are cut off during the Videosignal periods, the oscillation circuit 36, 3B maintains its own natural frequency during these periods. During the occurrence of the synchronizing impulses, however, the impedance reflected broadcast.

lected heterodyne-carrier output of frequency into the oscillation circuit 36, 38 by the frequency-adjusting networkv 3| is varied in accordance with the line-frequency and field-frequency impulse voltages applied to the grids of the tubes 40 and 4| from the generators I2 and I3 so that the frequency of the oscillation circuit is shifted to a value dependent upon whether a line-frequency or a field-frequency pulse is applied to the input circuits of tubes 40 and 4I.

The relationship of the line-synchronizing and field-synchronizing pulses is preferably as shown in Fig. 3 of the drawings in which the transmitted line-synchronizing signals are indicated as L and the transmitted field-synchronizing signals are indicated as F. The field-synchronizing pulses are of approximately half the amplitude of the line-synchronizing pulses but considerably longer in duration and preferably bear such relationship to the line-synchronizing pulses that pulses of the two types are never transmitted during the same time interval. The relationship of the succeeding field-synchronizing pulse to the line-synchronizing pulses in a double-interlaced scanning systern is shown by thedottedline pulse F'.

Since the oscillator 30 is coupled to the frequency changer 20, its output is mixed with the video-modulated carrier signal from Athe filter vI9 and the sum and difference heterodyne-frequency components are developed in the output circuit of the frequency changer 20 in a Well-known manner. Either the sum-frequency or the differencefrequency components are selected by the filter 2| and delivered to the power amplifier 22 to be Therefore, the frequency of the sechanger 2l) is maintained constant during the trace intervals but varied or shifted during the retrace intervals in correspondence with the frequency variations of oscillator 30, as described above. In Fig. 4, there is illustrated half of the envelope of the resultant amplitude-modulated carrier wave developed by the transmitting system. The video-frequency signal components are represented by the portions of the Wave indicated at V, the portions representing line-retrace and field-retrace periods, during which the carrier is shifted or varied, as described with reference to Fig. 3, being indicated at L and'F, respectively, and magnitudes ofthe frequency shifts of the carrier wave being represented by the pulses L by the video-signal components only during thel trace-scanning periods and, during these periods,

the frequency of the wave developed by generator 30 and supplied to frequency changer 28 is constant so that the carrier frequency of the signal output of frequency changer 20 is constant. During a portion of each line-retrace period an impulse from generator I2 is impressed on frequency-adjusting network 3|, thereby to effect a predetermined deviation in the frequency developed by the generator 3U and, hence, in that of the carrier frequency of the signal developed in frequency changer 20, as indicated by the pulses L of Fig. 3. Preferably, this frequency deviation is many times the frequency of the linesynchronizing signals of the system and may be, for example, of the order of 2 megacycles for a carrier frequency of 50 Inegacycles. portion of each field-retrace period, on the other hand, an impulse from the generator I3 is applied to network 3|, thereby toeifect a different and lesser predetermined frequency deviation in l During a the frequency developed by oscillator 30 and,

hence, in thatof the carrier frequency of the signal output offrequency changer 20, as indicated by the pulse" F of Fig. 3. Line synchronization of the system, as will be seen by the curves of Fig. 3, is not interrupted during field-retrace periods.

AReferring now to Fig. 2, the system there illustrated comprises a receiver of the superheterodyne type for receiving and utilizing the signal developed by the transmitter ofFig. 1 or a modulated-carrier wave including video-signal components amplitude-modulated on the carrier wave only during trace intervalsand synchronizing-signal components frequency-modulated on the carrier wave only during retrace intervals. This receiver includes an antenna system 5|), 5| to which there are connected in cascade, in the order named, a radio-frequency amplier and frequency changer 52, an intermediate-frequency amplifier 53, an amplitude detector 54, a video-frequency equalizer 90, a video-frequency amplifier 55, a unidirectional or background component reinserter 9|, and a cathoderay signal-reproducing device 56'. Preferably, as explained below, the .stages 52 and 53 are designed for single-sideband reception. A linescanning generator 51 and a field-scanning generator 58 are also coupled to the output of amplifier 53 by way of synchronizing-signal deriving, apparatus 59 hereinafter described in more detail. The generators 51 and 58 are coupled' selectively amplified in the intermediate-frequency amplifier 53 and delivered to the detector 54. The video amplitude-modulation components of the signal are derived by the detector 54 and are supplied through equalizer 90, the operation of which will be described in detail hereinafter, to the video-frequency amplifier 55, wherein they are amplified andfrom which they are supplied in the usual manner to a brilliancycontrol electrode of signal-reproducing device 56, the signals being Istabilized by background reinserter 9| in a manner to be hereinafter fully described. l

The intermediate-frequency signal is also supplied from the amplifier 53 to the apparatus 59 wherein the synchronizing signals are derived, the line-synchronizing and field-synchronizing components being effectively separated from the video-frequency signals and from each other and applied to the control circuits of the generators 51 and 58 as will be hereinafter further explained. Saw-tooth current or voltage scanning ywaves are developed in the line-scanning and field-scanning generators 51 and 58 and applied to the scanning elements of the signal-reproducing device 56 to produce electric scanning fields, thereby to deect the intensity-modulated cathoderay in two directions normal to combinations 95 and 96.

each other so as to trace successive series or fields of parallel lines on the target of the tube to reconstruct the transmitted image.

Referring now more particularly to the synchronizlng-signal deriving apparatus 59, there is comprised therein an intermediate-frequency amplifier 60 to which line-scanning generator 5l is coupled through a line-frequency selector 8| and a rectier and amplitude selector 83 and to which eld-scanning generator 58 is coupled through a held-frequency selector 82 and a rectiiier and amplitude selector 84. The line-frequency selector 8| comprises a double-tuned selector circuit 92, 93 and is eiective to pass primarily the carrier wave when deviated by the line-synchronizing pulses' L of Fig. 3, which selected wave pulses are rectified in rectifier and amplitude selector 83. Unit 83 comprises a di.

ode rectier having a load circuit having two time constants, due to the resistor-condenser The time constant of the combination is long relative to-the period of fore, the video-frequency signal of the receiver receive video-signal components which arel negatively amplitude-modulated on the received carrier, background reinserter 9| is effective to stabilize the signal input to signal-reproducing device 56 at an amplitude level thereof corresponding to the black shade value of the transmitted signal, rather than at some infra-black level as in conventional television systems. On

` the other hand, if the received'video-signal comthe line pulses and serves to provide a bias for amplitude range of the output of unit 83'comprising substantially only line-synchronizing signal information. Similarly, held-frequency selector 82 .is effecvtive to pass primarily the carrier wave when deviated by the field-synchronizing pulses F of Fig, 3, .which selected wave pulses are rectified by rectifier and amplitude selector 84. Only the peaks of the rectied output of amplitude selector unit 84 are utilized to synchronize fieldscanning generator 58, whch comprises substantially only eld-synchronizing signal information.

In considering the operation of the system just described, it will be assumed that both the singlesideband filter i9 of Fig. l and the selector of intermediate-frequency amplier 53 of Fig. 2, which may be of any suitable well-known design, have characteristics, such 'as is shown by curve A of Fig. 5, wherein the relative gain is plotted against frequency. The' selector is designed to have a response characteristic which is substantially level or uniform over a wide frequency band and a mean frequency so related to the carrier frequency of the signal to be translated that this .carrier frequency is located on the uniform portion thereof, as indicated at X in Fig. 5. The selectors thus pass the carrier wave and one complete sideband of its modulation components, a portion of the other sideband components being suppressed by the selectors. It will be seen that, inasmuch as the carrier frequency of the system is at all times located upon the uniformresponse portion of the characteristic selective circuits of the system, there is substantially no amplitude change in theintermediate-frequency signal output of amplifier 53 due to the frequency shift of the carrier wave duringthe lineponents are positively modulated on the received carrier, background reinserter 9| is effective to stabilize the -signal input to signal-reproducing device 56 at an amplitude level corresponding to the White shade value of the transmitted signal. If the receiver is adapted to receive such positively-modulated video signals, it is necessary that the scanning generators 5l and 58 also supply to signal-reproducing device 56 block-out pulses for causing the scanning beam to be blocked out during the retrace'intervals of the system,

Background reinserter 9| may be of conven- -tional form and comprise a diode 9`| having a load circuit including resistor 98 which is effective, together with source 99, to provide a suitable operating bias for signal-reproducing device 56, the unidirectional component of amplifier being blocked by condenser 96.

However, inasmuch as in the receiver of Fig. 2

the double-sideband components corresponding to the lower modulation-frequency components and adjacent the carrier frequency are translated With substantially the same gain as the pure single-banded components, the detector output at the lower modulation frequencies is greater than that at the higher modulation frequencies. Therefore, it is necessary to provide an equalizer 98 having 1a .band-pass characteristic, substantially as represented bycurve B of Fig. 6, which is effective relatively to equalize the reproduced video-frequency components of retrace and field-retrace intervals of the signal. y

`and. amplitude-modulated by the video-signal components during retrace intervals. Therethe transmitted picture. For this purpose, the relative gain of equalizer 9|) between zero frequency and a frequency fn, corresponding to the video-signal range over which double-sideband components are transmitted and received, is haii that ofthe video-signal range fa to fb, which corresponds to that over which only singlesideband components areA transmitted and -received. Such a band-pass characteristic may be provided by including a selective attenuator circuit in equalizer 99. Thus, resistorsY mi and |62 may constitute a potentiometer to halve the amplitudes of components in the frequency range 'zero to fa, while condenser |193 is of such value that it by-passes resistor im and thus removes the attenuation for components in the frequency range fs to fb.

lt will be understood that equalizer 9B may be omitted,-providing la corresponding amplitude compensation is made in the video-frequency portion of the transmitter of Fig. 1. In such case, the received signal may still be stanizing signals causes no amplitude variation` which may later appear in the received and detected video-frequency signal.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore,

transmitted picture and means for stabilizing the signal input to said reproducing device at an amplitude level corresponding to said limiting shade value of the transmitted picture.

3. A television signal receiver adapted to receive a modulated-carrier wave including videosignal components negatively amplitude-modulated on said carrier wave only during trace intervals and synchronizing components frequencymodulated on said carrier Wave only during retrace intervals comprising, means for detecting and utilizing said frequency-modulated compol nents to synchronize the scanning operation of aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A television signal receiver adapted to re- -ceive a modulated-carrier wave including videosignal components amplitude-modulated on said carrier Wave only during trace intervals and synchronizing components frequency-modulated on said carrier wave only during retrace intervals comprising, means for detecting and utilizing said frequency-modulated components to synchronize the scanning operation of said receiver,

means for deriving from said received carrier signal a carrier signal having a peak-amplitude level during said retrace intervals representative of a limiting shade value of the transmitted picture and amplitude-modulated by said Videosignal components during said trace intervals, and means including a reproducing device for detecting andv utilizing said amplitude-modulation components of said derived carrier signal,

said detected amplitude-modulation components being subject to variation in amplitude in accordance with received carrier-Wave amplitude variations, said last-named means including means for stabilizing the signal input to said reproducing device at an amplitude level corresponding to said limiting shade value of the transmitted picture.

2. A television signal receiver adapted to receive a modulated-carrier wave including videosignal components amplitude-modulated on said carrier wave only during trace intervals and synchronizing components frequency-modulated.

on said carrier Wave only during retrace intervals comprising, means for detecting and utilizing said frequency-modulated components to synchronize the scanning operation of said receiver, means for deriving from said received carrier signal a carrier signal having a peak-amplitude level during said retrace intervals represensaid receiver, means for deriving from said received carrier signal a carrier signal having a peak-amplitude level during said retrace intervals representative of the black shade value of the transmitted picture and amplitude-modulated by said video-signal components during trace intervals, and means including a reproducing device for detecting and utilizing said amplitude-modulation components of said derived carrier signal, said detected `amplitude-modulation components being subject to variation in amplitude in accordance with received carrier-wave amplitude variations, said last-named means including means for stabilizing the signal input to said reproducing device at the signal amplitude corresponding to said black shade value of the transmitted picture.

4. A television signal receiver adapted to receive a modulated-carrier wave including videosignal components positively amplitude-modulated on said carrier Wave only during trace intervals and synchronizing components frequencymodulated on said carrier Wave only during retrace intervals comprising, means for detecting and utilizing said frequency-modulated components to synchronize the scanning operation of said receiver, means for deriving from said received carrier signal a carrier signal having a peak-amplitude level during said retrace intervals 'representative of the White shade value of the transmitted lpicture and amplitude-modulated by said video-signal components during trace intervals, means including a reproducing device for detecting and utilizing said amplitude-modulation components of said derived carrier signal, said detected amplitude-modulation components being subject to variation in amplitude in accordance with received carrier-wave amplitude variations, said last-mentioned means including means for stabilizing Athe signal input to said reproducing device at the amplitude level corresponding to said white-shade value of the transmitted picture, and means responsive to said synchronizing means to block out said reproducing device during the retrace interval of the scanning cycle.

5. A television signal receiver adapted to receive a modulated-carrier wave amplitude-modulated by video-signal components only during trace intervals and frequency-modulated by line-synchronizing pulses to a predetermined deviation only during line-retrace intervals and by field-synchronizing pulses to a deviation of lesser magnitude during field-retrace intervals comprising, a selective circuit responsive to said linesynchronizing carrier deviations, a selective circuit responsive to said field-synchronizing carrier deviations, means coupled to said iirst-mentioned selective circuit for deriving line-synchronizing signals for said receiver, means coupled i-o said last-mentioned selective circuit for derivi ng field-synchronizing signals for said receiver, means for deriving from said received carrier signal a carrier signal having a peakamplitude level during said retrace intervals representative of a limiting shade value of the transmitted picture and amplitude-modulated by said video-signal components during said trace intervals, and means including a reproducing device for detecting and utilizing said amplitudemodulation components of said derived carrier signal, said detected amplitude-modulation components being subject to variation in amplitude in accordance with received carrier-wave amplitude variations, said last-mentioned means ncluding means ior stabilizing the signal input to said reproducing device at an amplitude level corresponding to said limiting shade value of the transmitted picture.

` 6. A television signal yreceiver adapted to receive a modulated-carrier Wave amplitude-modulated by video-signal components only during trace intervals and frequency-modulated by line-synchronizing pulses to a predetermined deviation only during line-retrace intervals and by eld-synchronizing pulses to a deviation of lesser magnitude during field-retrace intervals comprising, a selective circuit responsive to said linesynchronizing carrier deviations, a selective circuit responsive to said held-synchronizing carrier deviations, amplitude-selecting means coupled to said rst-mentioned selective circuit for selecting amplitude values thereof above a predetermined value to derive line-synchronizing signals for said receiver, amplitude-selecting means coupled to said last-mentioned selective circuit for selecting amplitude values above a predetermined value to derive eld-synchronizing signals for said receiver, means for deriving from said received carrier signal a carrier signal having a peak-amplitude level during said retrace intervals represenative of a limiting shade value of the transmitted picture and amplitude-modulated by said video-signal components during said trace intervals, and means including a reproducing device for detecting and utilizing said amplitudemodulation components of said derived carrier signal, said detected amplitude-modulation components being subject to variation in amplitude in accordance with received carrier-Wave amplitude variations, said last-mentioned means including means for stabilizing the signal input to said reproducing device at an amplitude level corresponding to said limiting shade value of the transmitted picture.

7. A television signal receiver adapted to receive a modulated-carrier wave including videosignal components amplitude-modulated on said carrier wave as partially double-sideband and partially single-sideband components only during trace intervals and synchronizing components frequency-modulated on said carrier Wave only during retrace intervals comprising, means for detecting and utilizing said frequency-moluuated components to synchronize the operation of said receiver, means for deriving from said received carrier signal a carrier signal having a peakamplitude level during said retrace intervals representative of a limiting shade value of the transmitted picture and amplitude-modulated by said video-signal components during said trace intervals, means for detecting said amplitudemodulation components of said derived carrier signal, means coupled to said last-mentioned detecting means for translating amplitude-modulation components corresponding to double-sideband reception with a relative gain of half that of components corresponding to single-sideband reception, said detected amplitude-modulation components being subject to variation in amplitude in accordance with received carrier-Wave amplitude variations, means for reproducing vsaid detected amplitude-modulated components, and means for stabilizing the signal input to said reproducing means at an amplitude level corresponding to said limiting shade value of the transmitted picture.

8. A single-sideband television receiver adapted to receive a modulated-carrier wave including double-sideband and single-sideband videosignal components relatively equalized at the transmitter and amplitude-modulated on said carrier wave only during trace intervals and synchronizing components frequency-modulated on said carrier wave only during retrace intervals comprising, means for utilizing said frequencyhaving a uniform gain over its frequency passv band for amplifying said detected amplitudemodulation components, means for reproducing said detected amplitude-modulated components, and means for stabilizing the signal input to said reproducing device at an amplitude level corresponding to said limiting shade value of the transmitted picture.

9. A television signal receiver adapted to receive a modulated-carrier Wave including videosignal components amplitude-modulated on said carrier Wave only during trace intervals and synchronizing components frequency-modulated on said carrier Wave only during retrace intervals comprising, means for detecting and utilizying said frequency-modulated components to synchronize the scanning operation of said receiver, means for deriving from said received carrier signal a carrier signal having a peakamplitude level during said retrace intervals representative of a limiting shade value of the transmitted picture and amplitude-modulatedby said video-signal components during said trace intervals, and means including a reproducing device for detecting and utilizing-said amplitudemodulation components of said derived carrier signal and including means for providing singlesideband equalization for video components sn located as to cause no conversion of received frefluency-modulation components to amplitudemodulation components, said detected amplitudemodulation components being subject to variation in amplitude in accordance with received carrier-Wave amplitude variations, said means including said reproducing device including means for stabilizing the signal input to said reproducing device at an amplitude level corresponding to said limiting shade value of the transmitted picture.

ARTHUR V. LOUGHREN. 

